The present invention relates to an optical-signal transmission apparatus and a method for optical signal transmission, and a signal processing apparatus for signal processing including optical signal transmission.
The function of a circuit board used in a data processing system (daughter board) is increasing by virtue of development of very large-scale integrated circuit (VLSI). With the increase in circuit function, the number of signals connected to respective circuit boards increases, and therefore, a parallel architecture requiring a number of connectors and connection lines is adopted as a data bus board (mother board) connecting the respective circuit boards (daughter boards) with a bus structure. The parallel architecture is developed by multilayered and miniaturized connection lines so as to improve the bus operation speed. However, signal delay due to capacity between connection wires and resistance of the connection wire lowers bus operation speed, and the system processing speed is restricted by the bus operation speed. Further, a problem occurs when the apparatus heats with increase in electric consumption. Further, as transmission-waiting time due to bus occupation influences the system processing speed, there is a need for simultaneous transmission among a plurality of circuit boards. Furthermore, the problems of EMI (Electromagnetic Interference) noise due to high-density bus-connection wiring seriously disturb improvement in the system processing speed.
That is, as the bus operation speed is limited, the number of the bus wires is increased in correspondence with increase in data transmission amount. However, as the number of wires increases, the electric consumption increases, further, transmission speed reduces due to skew between wires and further, there is a problem in wiring space. Japanese Published Unexamined Patent Application No. Sho 64-14631 and Hei 8-328707 disclose analog bus connection to reduce the number of wires among devices and facilitate wiring.
FIG. 13 shows an example of the analog bus connection disclosed in Japanese Published Unexamined Patent Application No. Hei 8-328707.
Apparatuses 401 and 411 are interconnected by an analog bus 406 via two A/D converters 404 and 407 and two D/A converters 405 and 408.
An n-bit signal generated from the apparatus 401 is introduced via a transmission path 403 into the D/A converter 405, converted into analog data, and transmitted onto the analog bus 406. The data passed through the analog bus 406 is converted into an n-bit digital signal by the A/D converter 407, and transmitted via a transmission path 409 into the apparatus 411. On the other hand, a signal transmitted from the apparatus 411 is transmitted via a transmission path 410 into the D/A converter 408, converted into analog data, and transmitted onto the analog bus 406. The data passed through the analog bus 406 is converted into a digital signal by the A/D converter 404, and transmitted via a transmission path 402 into the apparatus 401.
As described above, the analog bus 406 operates with a multilevel analog signal, and the apparatuses 401 and 411 operate with a digital signal.
In the analog bus connection as described above, as the signal that passes through the analog bus 406 is a multilevel analog signal, level change occurs due to a bus-line resistive component, a leak current and the like. If the analog bus line is prolonged or a number of apparatuses are connected to the analog bus, data transmission cannot be accurately performed without difficulty.
Further, microcomputers and the like often use a plurality of buses in addition to connection with a number of functional blocks. In such case, as communication cannot be made among the plurality of buses, the above-described analog bus connection cannot be realized without difficulty. To solve this problem, Japanese Published Unexamined Patent Application No. Hei 8-328707 proposes a circuit to compensate the level change of analog bus. However, since an electric wire is used as the bus line, this is not a substantial solution of the problem to prevent the level change due to wiring resistance. Further, the problems of increase in electric consumption in case of high-speed bus drive and the skew of parallel wiring for large-capacity transmission cannot be solved. Further, in the case where the electric wire is used as the bus line, even if a multilevel-logic analog bus is employed, although simultaneous multiplex transmission can be performed in the same direction, bidirectional simultaneous multiplex transmission cannot be performed.
To realize high-speed transmission, utilization of an intra-system optical connection technique, i.e., so-called optical interconnection, instead of electric transmission technique is studied. The optical interconnection technique has been proposed by Teiji Uchidata (in The 9th Circuit Packaging Scientific Lecture Meeting), H. Tomimuro, et al., (xe2x80x9cPackaging Technology for Optical Interconnectsxe2x80x9d, IEEE Tokyo, No. 3, pp. 81-86, 1994), and Osamu Wada (Electronics 1993 April., pp. 52-55), as various applications in accordance with the content of system construction.
As one of the proposed various optical interconnection techniques, Japanese Published Unexamined Patent Application No. Hei 2-41042 discloses a data bus employing an optical data transmission method using high-speed and high-sensitivity light-emission/photoreception devices. In this example, a serial optical data bus for loop transmission between respective circuit boards is proposed. The circuit boards respectively have a light-emission/photoreception device on both front and rear surfaces, such that the light-emission/photoreception devices on adjacent circuit boards installed in a system frame are optically connected. In this method, signal light sent from one circuit board is photoelectric-converted by an adjacent circuit board, and the signal light is further electrolight-converted by the circuit board, and sent to the next adjacent circuit board. In this manner, the respective circuit boards, sequentially and serially arranged, transmit signal light through all the circuit boards by repeating photoelectric conversion and electrolight conversion. By this arrangement, the signal transmission speed depends on the conversion speed of the photoelectric conversion and electrolight conversion by the light-emission/photoreception devices on the circuit boards, and at the same time, is limited by the conversion speed. Further, as data transmission among the circuit boards is made by using optical connection via free space by the light-emission/photoreception devices on the respective circuit boards, all the circuit boards must be optically positioned with the light-emission/photoreception devices on both front and rear surfaces of the circuit boards and the circuit boards must be optically connected. Further, as the optical connection is made via the free space, interference (cross talk) occurs between adjacent optical transmission paths, which may disturb data transmission. Further, data transmission failure might occur by scattering of signal light due to conditions within the system such as dust. Further, as the respective circuit boards are serially arranged, the connection is released if any of the boards is removed, and a spare circuit board to compensate for the lack of removed is required. That is, the circuit boards cannot be freely added or removed, and the number of circuit boards is fixed.
Japanese Published Unexamined Patent Application No. Sho 61-196210 discloses a data transmission technique among circuit boards utilizing a two-dimensional array device. According to this technique, a plate is provided opposing to a light source having two parallel surfaces, and circuit boards are optically connected via a light path formed by a diffraction grating and a reflection device provided on the plate. However, this method merely connects light emitted from one point to one fixed point, and cannot connect all the circuit boards as in the above-described electric bus. Further, as a complicated optical system is required and positioning is difficult, interference (cross talk) may occur between adjacent optical data transmission paths due to positional shift of optical devices, which may cause data transmission failure. Further, as the connection information between circuit boards is determined by the diffraction grating and the reflection device on the plate surface, the circuit boards cannot be freely added or removed resulting in low extensibility of the system.
Japanese Published Unexamined Patent Application No. Hei 4-134415 discloses another data transmission between circuit boards utilizing the two-dimensional array device. According to this technique, a system which comprises a lens array of a plurality of lenses having a negative curvature formed on the surface of transparent material having a refractive index higher than that of air, and an optical system for introducing light which is generated from a light source from the side surface of the lens array, is provided in the transparent material. Further, there is also disclosed another system having a region of low refractive index or a hologram instead of the plurality of lenses having the negative curvature. In this method, light that enters from the side surface is diffused by the plurality of lenses, the region of low refractive index or the hologram, on the surface, and emitted. Accordingly, the intensity of output signal may vary in correspondence with the relation between the entrance position and emission positions on the surface with the plurality of lenses, the low refractive-index region or the hologram. Further, as optical input devices of circuit boards must be provided at the positions of the plurality of lenses having negative curvature, the low refractive-index region or the hologram, there is no freedom in arrangement of the circuit boards resulting in low extensibility of the system. As a means of solving these problems, a sheet-shaped optical data bus which transmits diffused signal light is considered. In use of this sheet-shaped optical data bus, the number of circuit boards is not limited, unlike the method in Japanese Published Unexamined Patent Application No. Hei 2-41042, further, the difficulty in optical positioning of the light-emission/photoreception devices as in Japanese Published Unexamined Patent Application No. Sho 61-196210 can be solved.
However, all of the above-described optical transmission methods merely convert a signal from an electronic circuit into an optical signal and transmit the converted optical signal, and are seriously limited by the electronic circuits.
Further, Japanese Published Unexamined Patent Application No. Hei 9-98137 discloses bidirectional communication via an optical fiber using optical signals having different wavelengths.
However, in this method, even though the bidirectional communication is made via the same optical fiber, the communicable range is limited between terminals with light-emitting devices and photoreception devices for transmitting and receiving light of one wavelength. To freely perform communication among a number of terminals, a plurality of light-emitting devices and photoreception devices must be provided in the respective terminals for handling light having various wavelengths, which complicates the apparatus""s structure and increases the cost.
That is, a technique to reduce the number of wires among terminals so as to facilitate wiring and to freely perform communication among a number of terminals has not been applied in any of electronic circuits and optical circuits.
The present invention has been made to solve the above problems, and has its object to provide an optical-signal transmission apparatus and a method which connect a number of terminals (apparatuses, circuit boards and the like) and freely perform communication among the plurality of terminals, and a signal processing apparatus using the optical-signal transmission method.
According to one aspect of the present invention, the foregoing object is attained by providing an optical-signal transmission apparatus comprising:
an optical transmission medium that transmits an optical signal, having a plurality of transmission nodes to input signal light into the optical transmission medium and at least one reception node to output an optical signal from the optical transmission medium;
a plurality of optical-signal transmission units, provided in correspondence with the respective transmission nodes, that respectively generate an optical signal and input the generated optical signal from the corresponding transmission node into the optical transmission medium, and generate pulse string optical signals having different light intensity levels among a plurality of optical-signal transmission units; and
an optical-signal reception unit, provided in correspondence with the reception node, that obtains a reception signal by obtaining the optical signal transmitted from the reception node, and separates a signal component corresponding to an optical signal generated by a desired optical-signal transmission unit, from among a plurality of signal components corresponding to the plurality of optical signals generated by the optical-signal transmitting units, included in the obtained reception signal.
Further, according to another aspect of the present invention, the foregoing object is attained by providing an optical-signal transmission apparatus comprising:
an optical transmission medium that transmits signal light, having at least one transmission node to input signal light into the optical transmission medium and a plurality of reception nodes to output signal light from the optical transmission medium;
an optical-signal transmission unit, provided in correspondence with the transmission node, that generates a plurality of pulse string optical signals having different light intensity levels or generates a multiplex pulse string optical signal where a plurality of pulse string optical signals having different light intensity levels are overlaid, and inputs the optical signals or multiplex optical signal from the corresponding transmission node into the optical transmission medium; and
an optical-signal reception unit, provided in correspondence with the respective reception nodes, that obtains a reception signal by obtaining the optical signals or multiplex optical signal transmitted from a corresponding reception node, separates a signal component corresponding to an optical signal generated by a desired optical-signal transmission unit, from among a plurality of signal components corresponding to the plurality of optical signals generated by the optical-signal transmitting unit, included in the obtained reception signal.
In the optical-signal transmission apparatus according to the second aspect of the present invention, in a case where the optical-signal transmission unit generates a multiplex pulse string optical signal where a plurality of pulse string optical signals having different light intensity levels are overlaid, any process may be used for finally obtaining the multiplex pulse string optical signal. For example, the multiplex pulse string optical signal may be obtained by generating a multiplex pulse string electric signal where a plurality of pulse string electric signals having different signal intensity levels and converting the multiplex pulse string electric signal into an optical signal. Alternatively, the multiplex pulse string optical signal may be obtained by converting a plurality of pulse string electric signals having different signal intensity levels into pulse string optical signals and overlaying the pulse string optical signals.
Further, according to another aspect of the present invention, the foregoing object is attained by providing an optical-signal transmission method comprising the steps of:
simultaneously introducing a plurality of optical signals having different light intensity levels or a multiplex optical signal where a plurality of optical signals having different light intensity levels are overlaid into an optical transmission medium that transmits signal light;
obtaining a reception signal by receiving the optical signals or multiplex optical signal transmitted from the optical transmission medium; and
separating a signal component corresponding to a desired optical signal from the reception signal.
Further, according to another aspect of the present invention, the foregoing object is attained by providing a signal processing apparatus comprising:
an optical transmission medium that transmits signal light, having a plurality of transmission nodes to input signal light into the optical transmission medium and at least one reception node to output an optical signal from the optical transmission medium;
a first circuit board sharedly carrying a plurality of optical-signal transmission units that respectively emit an optical signal, and generate a plurality of pulse string optical signals having different light intensity levels for respective optical-signal transmission units;
a second circuit board sharedly carrying a plurality of optical-signal reception units that obtain a reception signal by receiving the optical signals or multiplex optical signal, and separate a signal component corresponding to an optical signal generated by a desired optical-signal transmission unit, from among a plurality of signal components corresponding to the plurality of optical signals generated by the plurality of optical-signal transmission units, included in the obtained reception signal;
a support member that supports the first circuit board and the second circuit board positioned with respect to the optical transmission medium such that the optical signals generated from the optical-signal transmission units on the first circuit board are introduced from the transmission nodes into the optical transmission medium and signal light transmitted from the reception node is transmitted into the optical-signal reception unit on the second circuit board.
Further, according to another aspect of the present invention, the foregoing object is attained by providing a signal processing apparatus comprising:
an optical transmission medium that transmits signal light, having at least one transmission node to input signal light into the optical transmission medium and a plurality of reception nodes to output signal light from the optical transmission medium;
a first circuit board carrying an optical-signal transmission unit that simultaneously generates a plurality of pulse string optical signals having different light intensity levels or a multiplex pulse string optical signal where a plurality of pulse string optical signals having different light intensity levels are overlaid, and outputs the optical signals or multiplex optical signal;
a second circuit board carrying a plurality of optical-signal reception units that obtain a reception signal by receiving the optical signals or multiplex optical signal, and separate a signal component corresponding to a desired optical signal from among a plurality of signal components corresponding to the plurality of optical signals, included in the obtained reception signal;
a support member that supports the first circuit board and the second circuit board positioned with respect to the optical transmission medium such that the optical signals generated from the optical-signal transmission unit on the first circuit board are introduced from the transmission node into the optical transmission medium and the signal light transmitted from the reception nodes is transmitted into the optical-signal reception units on the second circuit board.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which reference characters designate the same name or similar parts throughout the figures thereof.